Typically, a LED (light emitting diode) is a semiconductor device that emits light when current flows, and converts electrical energy into light energy using a PN junction diode including GaAs and GaN optical semiconductors. The LED may radiate light with high efficiency at low voltage, thus making it usable in various electronic apparatuses such as home appliances, electronic display boards, and displays.
An LED lighting module typically includes a substrate or a printed circuit board including a conductive layer and an insulating layer. The insulating layer may typically include an insulating material having a predetermined thermal conductive property, such as a thermosetting resin. However, the LED lighting module needs to have excellent thermal conductivity in a vertical direction, but the thermal conductivity of the insulating layer in a vertical direction is not excellent even though the insulating layer includes a material having thermal conductivity, and accordingly, when light is emitted, the light emission efficiency of an LED chip is reduced due to an increase in the temperature, and the defect ratio of the LED lighting module is increased due to heat stress.
A resin used in the LED lighting module has low thermal stability in a relatively high temperature environment, whereby the demand for the development of an LED lighting module that does not include resin is growing. In connection therewith, it is most important to increase the strength of adhesion between a substrate and an electrode. The strength of adhesion between two materials is a very important property in determining the long-term reliability of the lighting. Particularly, the strength of adhesion may be very important in the development of a high-quality high electric power module, which is currently demanded in the lighting field.
Metal having excellent thermal stability and oxidation stability is frequently used to manufacture the lighting module that does not include resin, thus increasing the area of metal exposed on the surface of the module. For white light emission, a fluorescent substance is used, and accordingly, much light is reflected by the fluorescent substance. It is possible to manufacture an lighting module having high efficiency only when reflected light is reflected back to the outside of the module to be extracted. Therefore, the reduction in the secondary reflection ratio attributable to the use of metal having low reflectivity needs to be solved.